1. Field of the Invention
The present invention relates to modified magnetron high-frequency discharge plasma processing apparatuses, and in particular to apparatuses performing various kinds of processes using a plasma, plasma etching apparatuses for dry etching with a plasma, for example, films formed on the surface of a substrate to be processed, and plasma CVD (chemical vapor deposition) apparatuses for forming thin films on the surface of a substrate to be processed using gas phase reactions induced by a plasma.
2. Description of the Related Art
In recent years, plasma processing is increasingly used in the manufacturing process for a variety of semiconductor devices, liquid crystal displays, and solar batteries. The active species and ions generated in a plasma are used to etch a silicon oxide film formed on a silicon semiconductor as one method for dry etching, for example. With the increasing integration of semiconductor devices, wiring is laid out in multiple layers, so that insulating films between the wiring layers (interlayer insulating films) have to be provided. One known method for forming a film on the surface of a substrate is to introduce a reaction gas into the reaction chamber where the process is performed, and add heat to cause the gas to react. However, for this method, relatively high temperatures are necessary, so that there are many defects in the devices, and recently plasma CVD is often used, in which the energy that is necessary for the activation of the reaction is inferred by a plasma induced by glow discharge. Moreover, films for solar batteries are also formed by plasma CVD.
In dry etching, which is a typical plasma process, there is a need for uniform high-density plasmas suitable for substrates with larger surface areas with which the throughput of the apparatus can be increased, and for increased processing precision and selectivity, suitable for finer electronic device structures and a larger number of layers. There is also a need for plasmas with higher uniformity, so as to reduce charge-up damage. The development of a variety of plasma sources supposed to satisfy these needs is progressing.
However, although the density of plasmas generated with ECR (electron cyclotron resonance) plasma sources, ICP (inductively coupled plasma) plasma sources, and high-density plasma sources using surface microwaves plasma sources and helicon waves plasma sources is sufficient, it is currently impossible to ensure uniformity within Ø300 mm. In addition, in these high-density plasma sources, the electron temperature of the plasma has to be kept low, so as to suppress excessive ionization of the plasma gas. Especially with regard to etching silicon oxide films, high-density plasma sources addressing these requirements are still under development, and lower etching selectivity due to excessive ionization of the gas and charge accumulation at the substrate surface are still big problems.
In etching processes using current high-density plasma sources, the lower selectivity with respect to the underlying silicon when etching small silicon oxide film contact holes, undesired side etching due to charge build-up when etching gate polysilicon electrodes, and insulation breakdown of the gate oxide film are real problems. It seems that these phenomena are caused by large electron temperatures (that is, the presence of high-energy electrons) in the low-pressure high-density plasma. But low-pressure and high-density plasmas are necessary for plasma CVD processes.
It is an object of the present invention to provide a plasma processing apparatus, in which the uniformity of the plasma density can be increased, and the electron temperature can be kept low.
A plasma processing apparatus in accordance with the present invention includes a vacuum vessel made of a dielectric material, such as quartz or alumina, defining a plasma processing region in its inside; a gas supply/exhaust system that supplies/exhausts gas to/from the vacuum vessel; a tubular first electrode disposed around the periphery of the vacuum vessel and inducing discharges in the gas supplied to the vacuum vessel; a magnet disposed around the periphery of the vacuum vessel; and a high-frequency power apply system that applies high-frequency power to the tubular first electrode; wherein applying high-frequency power to the tubular first electrode generates a plasma inside the vacuum vessel. Here, xe2x80x9ctubularxe2x80x9d includes the shapes of, for example, circular, elliptical and polygonal rings, tubes and sleeves. The magnet can be a permanent magnet or an electromagnet, for example.
In accordance with this invention, gas is supplied by the gas supply system to the inside of the vacuum vessel, and the atmosphere inside the vacuum vessel is exhausted by the gas exhaust system. Moreover, a predetermined magnetic field is formed by the magnet. Furthermore, high-frequency power is applied by the high-frequency power apply system to the first electrode. Thus, a predetermined high-frequency electric field is formed. As a result, the electrons emitted from the first electrode are trapped in magnetron motion. Thus, a plasma having a high density is generated near the first electrode. Due to diffusion, a portion of this plasma moves toward the central portion of the plasma processing region. Thus, a plasma that has a high and uniform density is generated across the entire plasma processing region. As a result, it becomes possible to generate a plasma having a uniform density across a region of 30 mm diameter.
Moreover, in accordance with this invention, it is also possible to keep the electron temperature of the plasma low. Thus, the decrease of the etching selectivity and the charge density at the substrate surface can be reduced.
Furthermore, in accordance with this invention, the tubular first electrode does not form part of the wall of the vacuum vessel wall, because the tubular first electrode is arranged outside the vacuum vessel. Therefore, different to apparatuses in which a tubular electrode is sandwiched by portions of the vacuum vessel through insulating rings, it is not necessary to provide sealing members between the wall of the vacuum vessel and the insulating rings, and between the insulating rings and the tubular electrode. As a result, the assembly of the apparatus is simplified. Moreover, the number of sealed locations can be reduced, so that the apparatus is suitable for high vacuums in the vacuum vessel.
Furthermore, in accordance with the present invention, the surface of the first electrode can be prevented from contacting the plasma by arranging the first electrode outside the vacuum vessel. Thus, metal contamination caused when plasma damages are inflicted on the first electrode can be prevented.
Moreover, in the present invention, when the vacuum vessel is made of a dielectric material, such as quartz or alumina (Al2O3), plasma damages at the wall of the vacuum vessel as when the vacuum vessel is made of metal do not occur, and metal contamination of the substrate to be processed in the vacuum vessel caused by plasma damages can be effectively prevented.
From the above, in accordance with the present invention, metal contamination can be effectively avoided for processes near the gate, such as spacer films or gate dielectric films.
Furthermore, in accordance with the present invention, the vacuum vessel in the present invention is made of a dielectric material, so that there is no need to arrange a conducting material, such as an aluminum chamber, near the tubular first electrode. Therefore, electric power losses can be reduced considerably, and the efficiency of the plasma process can be improved.
It is preferable that the vacuum vessel comprises an upper vessel and a lower vessel, and that the upper vessel is dome-shaped and formed in one seamless piece, except that it has an open bottom portion. If the upper vessel is dome-shaped and formed in one seamless piece, then the assembly of the vacuum vessel becomes even easier.
It is preferable that the vacuum vessel has shower holes for uniformly supplying the gas, and that a susceptor, on which a substrate to be processed is placed, is arranged at a position facing the shower holes. With this configuration, the gas flow becomes uniform, and the substrate is plasma processed with greater uniformity.
It is preferable that a second electrode is arranged at an outer peripheral portion of the shower holes, outside the vacuum vessel. If high-frequency power is supplied jointly to the first electrode and the second electrode, then the plasma processing efficiency at the periphery of the processed substrate (the edge portion of a plasma processing region) can be controlled with the first electrode, and the plasma processing efficiency at the center of the processed substrate (the central part of the plasma processing region) can be controlled with the second electrode, so that the uniformity with which the substrate is plasma processed can be improved. Moreover, for the gas cleaning near the shower holes, the etching speed can be increased with the second electrode, thereby improving the cleaning efficiency.
It is also possible to arrange the second electrode not at an outer peripheral portion of the vacuum vessel portion provided with the shower holes, but on the inlet side of the shower holes, which is opposite the side of the plasma processing region of the vacuum vessel. If the plasma processing is plasma CVD processing, then a film is also deposited on the inside of the vacuum vessel, so that gas cleaning has to be performed regularly, and the film formation in the vacuum vessel is most pronounced near the shower holes. For the gas cleaning near the shower holes, the etching speed can be increased with the second electrode on the inlet side of the shower holes, which is opposite the side of the plasma processing region, thereby improving the cleaning efficiency.
If the second electrode is arranged on the inlet side of the shower holes, then it is preferable that the second electrode is in contact or proximity to a wall of the vacuum vessel that is provided with the shower holes, and that the second electrode is provided with gas flow holes at positions corresponding to the shower holes. With this configuration, when the second electrode is in contact or proximity to a wall of the vacuum vessel that is provided with the shower holes, gas can still be supplied from the shower holes without being obstructed by the second electrodes. Moreover, the cleaning efficiency can be improved even further, because the second electrode is in contact or proximity to a wall of the vacuum vessel.
It is preferable that the gas flow holes of the second electrode are larger than the shower holes. With this configuration, the flow of gas that is supplied through the shower holes is not obstructed, even when the positions of the gas flow holes of the second electrode with respect to the shower holes have shifted during assembly. Moreover, since the diameter of the shower holes provided on the side of the plasma processing region is not that large, abnormal plasma discharges do not occur.
The magnet can also be formed by arranging a plurality of permanent magnets around the vacuum vessel. With this configuration, the handling and the magnetization of the magnet is easier than if the magnet is made of only one magnet.
In this case, the plurality of permanent magnets can be held in place, for example, by providing a magnet holder having a plurality of fitting holes, and fitting the permanent magnets into the fitting holes of the magnet holder. With this configuration, it is easy to hold a plurality of permanent magnets in place.
Alternatively, it becomes possible to hold the plurality of permanent magnets in place by sandwiching them between the first electrode and a magnetic yoke forming a magnetic circuit. With this configuration, the operation of holding the plurality of permanent magnets in place can be performed easier than with the above-described configuration using a magnet holder. Moreover, the magnetic field in the circumferential direction of the vacuum vessel can be made more uniform than with the above-described configuration using a magnet holder. This is, because the plurality of permanent magnets can be lined up without gaps, and the permanent magnets can be provided with a rectangular or square profile. Moreover, the length of the permanent magnets (that is, the length in the direction connecting the two poles) can be made shorter than with the above-described configuration using a magnet holder. This is, because there is no need to secure the stroke for fitting the permanent magnets into the fitting holes. Thus, it becomes possible to make the permanent magnets plate-shaped. As a result, it becomes possible to make the apparatus smaller than with the above-described configuration using a magnet holder.